(1) Field of the Invention
The present invention relates to an improved ignition timing regulating apparatus for an internal combustion engine.
(2) Description of the Prior Art
To match the ignition timing of an internal combustion engine accurately to required engine performance, various kinds of electronically controlled apparatus for regulating ignition timing have been developed, in which a micro-computer is employed in place of a mechanically controlled device for regulating the advancing angle of ignition timing, or engine timing advance.
For example, a table of various time durations converted respectively from optimum ignition timing, these amounts correspond respectively to various operating conditions of the engine, for instance, the number of revolutions per unit time and the intake negative, is stored in the form of a pulse train, that is, a number of pulses representing the time duration, based on the fact that the advancing angle of ignition timing corresponds to the time duration elapsing from the timing of a standard engine angle. The advance angle corresponds to an operating condition of the engine, for instance, the number of revolutions per unit time (rpm), which is detected occasionally. A standard angle sensor is provided for deriving a standard angle signal at a predetermined angle of revolution of a crank, for instance, at every angle of 120 degress corresponding to the phase difference of ignition timing between each cylinder of a six cylinder engine. Thus, each time the standard angle signal is derived, the time duration representing the optimum ignition advance angle which corresponds to the occasionally detected operating condition of the engine, can be read out from the table, and when the time duration elapsing from the timing of the standard angle coincides with the above read out time duration, an igniting signal can be obtained.
According to the above example, the obtained optimum ignition timing advance angle corresponds to only the time duration elapsing from the timing of the standard angle which is responsive to the operating condition of the engine. Thus, it is occasionally not required to detect the crank angle precisely, and it is therefore possible to simplify the crank angle sensor for detecting the crank angle.
However, on the other hand, the above exemplified apparatus has such a defect that, until the number of revolutions per unit time, that is, the speed of revolution (rpm) of the engine can be detected, it is impossible at the starting of the engine, for instance, during engine cranking to determine the ignition timing at which the ignition should be carried out.
Thus, since detection of the speed of revolution can be performed by counting the time duration between successive timings of the aforesaid standard angle, the initial data relating to the speed of revolution cannot be obtained, until at least two of the aforesaid standard angle signals are derived from the standard angle sensor in response to one third of a revolution of the crank shaft. Initial ignition is thus apt to be unattainable during engine cranking, and as a result thereof the starting performance of the engine is deteriorated.
Further, the time duration, that is, the number of pulses of the pulse train to be counted each pulse represents the is increased during low engine speed in comparison with high engine speed, so that the number of bits of the data to be operated in the micro computer employed in the apparatus is increased with substantial disadvantage.